The manufacture of corrugated board essentially is to combine sheet linerboards with a corrugated medium by means of adhesives. However, too much heat energy is consumed in this operation because water-base starch glue, for which gelatin and concentration are carried out only through heating and drying, is used an adhesive.
In the manufacture of corrugated board, single-faced board is first made on a single facer.
That is, fed sheet medium is corrugated while starch adhesive is applied onto the tips of the flutes of said corrugated medium with an applicator roll, and sheet linerboard is bonded, by means of heat and pressure, on said medium to which starch adhesive has been applied.
Then, the single-faced board manufactured on said single facer is transported to a glue machine, wherein starch adhesive is applied onto the flute tips of said single-faced board, and is fed to between the canvas and the heat tables heated to about 170.degree. C. of a double facer. After said single-faced board is combined with fed double-faced linerboard for single-wall corrugated board, or fed double-faced linerboard and another single-faced board for double-wall corrugated board, weight rolls firmly press the combined board to canvas-covered heat tables to gelatinize and dry the adhesive. Thereafter, the resulting single-wall board or double-wall board is slit and scored on a slitter scorer, is cut into a given length on a rotary cutoff, and is converted into single-wall corrugated blanks or double-wall corrugated blanks.
The adhesion on the double facer is carried out by heating starch adhesive applied onto the flute tips of the single-faced board through double-faced linerboard for single-wall board or through double-faced linerboard and another single-faced board for double-wall board.
Further, since single-faced board having formed flutes is combined with double-faced linerboard on the double facer, high pressure can not be loaded on the combined board because of possible flute damage. These cause heat transfer efficiency at the heating tables to be extremely low. Therefore, much heat energy consumption in the double facer results in a severe problem.
In order to overcome the above defect, production processes for corrugated board which employ adhesives requiring no heating have been studied these past years (See Japanese Patent Laid Open Publication Nos. 32570/1981, 70074/1981 and 105952/1981). Furthermore, various studies have been carried out for polyvinyl alcohol type adhesives for paper (See Japanese Patent Publication No. 22579/1961, Japanese Patent Laid Open Publication No. 3336/1972 and U.S. Pat. No. 3,135,648 etc.).
However, as disclosed in the above-mentioned Japanese Patent Laid Open Publication Nos. 32570/1981 and 70074/1981, the so-called adhesives which can be applied to paper at a high temperature but which gelatinize upon cooling are those which use a property that the adhesive applied at a high temperature shows increasing viscosity and hardening upon cooling. Therefore, at low speed, there is a defect in that the adhesive applied onto the corrugated medium is hardened before being combined with linerboard, and that adhesion cannot be carried out.
Some set-back type starch adhesives containing a high content of amylose have an excellent setting property, but these adhesives have a defect that once adhesive is hardened upon cooling, it can not become fluid even if it is heated again. Then, such adhesives have a great problem in machinabilities such as conveying through pipes, applying, storing and the like, and can not be used in practical application.
On the other hand, Japanese Patent Laid Open Publication No. 105952/1981 discloses a method wherein adhesive is applied either onto corrugating medium or linerboard, and gelatinizing agents are coated onto the other. Thereafter, contact is carried out each other and adhesion is made by the reaction of the adhesive and the gelatinizing agents. However, this method has a defect that a process is complicated.
Polyvinyl alcohol type adhesives disclosed in Japanese Patent Publication No. 22579/1961, Japanese Patent Laid Open Publication No. 3336/1972 and U.S. Pat. No. 3,135,648 are insufficient in green bond, and manufacturing corrugated board at high speed could not be attained by the method which does not need heating at heat tables after application of adhesive.
Also, heat energy saving could not be accomplished.